Electrical equipment and devices, and in particular high voltage equipment in an electrical power distribution system, have high heat dissipation and therefore require adequate cooling. For example, a conventional HVDC (High-Voltage Direct Current) converter valve may be air insulated and water-cooled. A cooling system is conventionally provided comprising for example cooling water distribution pipes that are shaped to fulfill certain requirements. Another example of an external cooling system is the use of fans.
However, there are also electrical devices within a power distribution system that are not cooled by any external cooling system, such as the above-mentioned water distribution pipes. Those devices, lacking an external cooling system, are then instead just self-cooled, i.e. natural convective air-cooling. One example of such a self-cooled device is a converter transformer bushing.
Typical voltage levels within electrical power distribution systems range up to about 500 kV DC. However, the voltage levels increases constantly and may amount to as much as 800 kV DC and presumably even higher voltage levels in the future. Also, current levels may be up to 4000-5000 A or even higher. Naturally, such high voltages and current levels result in still higher heat dissipation and the requirements on electrical insulation of a bushing become extremely high. The size of the electrical insulation limits the cooling efficiency of the bushing, since the heat has to be led a longer distance to the ambient cooling air due to its increased size. The self-cooling is thus rendered insufficient at the very high voltage and current levels.
It would be feasible to utilize larger conductors when increasing the voltage levels, thereby lowering the heat dissipated, but this would again entail enlarging the equipment. That is, the size of the insulation would still be large.
In view of the above, it would be desirable to enable improved cooling of high voltage devices, such as high voltage bushings. Further, it would also be desirable to provide a corresponding method for cooling such bushings.
In pending (not yet published) PCT application SE2006/000977 filed Aug. 25, 2006, a water based cooling system of a high voltage bushing is described.